Now, I believe you can do either way.
I think how David Hund did it on his (one-page) site valuedstandards.com is fine. I am planning something similar for my web page.
Ultimately, so long as there is a (keyboardable, not relying on the user having a screen reader or some native appy thing) skip link to the "other" part of the page, it's good.
But, if the menu is short and sweet (just a few options), since traditionally menus came before the content, this is probably still a better idea just out of user experience.
Many sites have long crazy menus though. Especially if their "desktop" versions are dropdown menus. While on a wide screen this makes a long, complicated menu look short and sweet, tab-wise it's a monster. I'd much rather have those after the main content (even on a corporate guff page), though again only so long as there's an easy way to skip to the menu if I need to.
The only thing I think is silly is everyone jumping on some new iBandwagon going "ZOMG RESPONSIVE WEBSITES MUST HAZ MENU ON BOTTOM LAWLZ" without thinking it through, or doing user testing for your particular site (if it's large and corporate and it really matters and you might lose a boatload of money choosing the wrong solution blah blah)... but I think it can improve the user experience in some? many? cases.
I would like to try using a dropdown for mobiles, if I can make it accessible.
Hm, I'd be interested in knowing your solution if you come up with one. Touch Events come to mind, except lots and lots of mobiles don't support it, let alone those who don't even run JS at all, or well...
David's :target trick is cute but he deliberately didn't worry much about older IE's for example...